Welding wire is often supplied in the form of a coil contained in a container, the central axis of the coil being arranged vertically. The welding wire is withdrawn from the container by pulling the welding wire upwardly through a central opening of the container. Typically, a retainer is used which is placed on top of the coil and which prevents that the upper turns of the welding wire change their position in an uncontrolled manner such that tangles and knots could occur in the welding wire.
Automated welding and other industrial applications often require large quantities of wires to be stored in these containers, also referred to as bulk containers (drums or boxes with polygonal cross-section) with the scope of minimizing the production interruptions caused by pack changeovers. These bulk packs can, in some instances, carry up to 1,400 kg (approx. 3,000 lbs) of wire, and the wire can have diameters of up to 4.00 mm ( 5/32″). Since their introduction years ago, these bulk packages containing large quantities of twist-free torsion-less wires have become increasingly popular in many applications that exploit the benefits of robotic and automation in welding processes like GMAW (Gas Metal Arc welding) and SAW (Submerged Arc Welding) or have found their use in the metal spraying of wires for surface treatments and several other industrial applications.
Employing packs with larger dimensions in order to accommodate larger diameter wires involves however also the necessity to overcome a few technical problems like the difficulty to effectively maintain all the wire strands in control while a single wire is being paid out from the pack, and prevent them from exiting the packs simultaneously and uncontrolled with consequent tangles and unwanted production stops which would offset the downtime savings achieved by bulk quantities in the pack. Weld bead interruptions caused by poor feeding or tangled wires can, in some cases, negatively affect the mechanical properties of the finished welded parts rendering them unfit for sale with considerable economic damages for the manufacturer. As previously explained, tangling can occur when a few wire strands are not properly grasped by the retainer and they can freely fall into the center of the drum or pack from where they feed in an uncontrolled and disorderly manner.
It is obvious that the larger the inner diameter of the drums or containers, the more and more difficult it is to control the strands of wire with the conventional retainers known so far.
Bulk pack retainers are commonly employed today in the industry and they come in different forms ranging from ring shaped plane plates to cone shaped plates and metal cages but they all have in common the fact that they are rigid pieces. Consequently, especially with thicker and therefore stiffer wires which exert a lot of pressure upward, the wire being paid out from the pack can lift the one-piece rigid retainer and involuntarily cause the uncontrolled release of other wire strands which can freely escape from underneath the retainer itself, and jam.
Some of the prior art solutions like those shown in U.S. Pat. Nos. 5,746,380 or 7,004,318 attempt to provide a dynamic retainer which interacts with the payout of the wire. However, in order to function and for the retainer and the retaining elements not to be dragged or fall into the center of the drum or pack, they must rely on a centre core provided in the container, which represents itself a feeding obstacle for the wire, specially in the lower half of the drum/pack. More specifically, both solutions shown in these documents appear to be totally useless with thick wires which are characterized by a high “columnar” strength, since these retainers are not strong enough to keep the wire strands down and under control. If the retainer weight however is intentionally increased in an attempt to compensate the increased pressure strength of thicker wires, they end up deforming the single wire strand being paid out with a negative effect on the precision of the weld placement. Testing at Wind Tower manufacturing sites showed that softer Submerged Arc welding wire, like SAW UNI EN 756:04 grade S2 (AWS A5.17:07 grade EM12K) even in a 4.00 mm diameter can easily be bent and deformed by a rigid heavy retainer with consequent “wavy” defects and irregular weld beads, which are totally unacceptable for the quality and safety standards required by such application.
US 2011/0114523 shows a solution which, although it comes with benefit that a centre core is not required, proposes a self-adapting rubber retainer with multiple flexible stripes. However, manufacturing costs are an issue here since, in order to stay placed on the wire coil and not to slip into the centre of the drum/pack, it must be attached to a supportive outer rigid frame. The cost of molding or assembling two materials (one rigid and one flexible) for the same retainer would negatively impact the price of the wire contained in the pack. Moreover, the rigid outer supporting frame still makes the flexible retainer behave like a rigid one and such solution is technically impossible with packs having a diameter as large as 1,000 mm (3.28 ft).
US 2011/0094011 shows a rigid panel with four flexible rubber fingers at the corners. This solution also requires a composed retainer which is more expensive to produce but it is definitely unsuitable for controlling and braking of thicker wires ranging from 2.00 to 4.00 mm in diameter, as normally used in the SAW (Submerged Arc Welding) applications.
Accordingly, there is a need for a retainer which can be produced at low costs but at the same time allows to reliably prevent entanglement and unintentional lifting of the upper turns of the wire from the coil.